Dual-anode electrolytic capacitor for use in an implantable medical device

ABSTRACT

A capacitor structure having a shallow drawn encasement includes first and second major sides and a peripheral wall coupled to first and second major sides. First and second anodes are positioned within the encasement proximate the interior surfaces of the first and second major sides respectively. A cathode is positioned within the encasement intermediate the first and second anodes.

FIELD OF THE INVENTION

The present invention generally relates to capacitors, and moreparticularly to a thin dual-anode electrolytic capacitor suitable foruse in an implantable medical device such as an implantable cardiacdefibrillator (ICD).

BACKGROUND OF THE INVENTION

ICDs are devices that are typically implanted in a patient's chest totreat very fast, and potentially lethal, cardiac arrhythmias. Thesedevices continuously monitor the heart's electrical signals and senseif, for example, the heart is beating dangerously fast. If thiscondition is detected, the ICD can deliver one or more electric shocks,within about five to ten seconds, to return the heart to a normal heartrhythm. These defibrillation electric shocks may range from a fewmicro-joules to very powerful shocks of approximately twenty-five joulesto forty joules.

Early generations of ICDs utilized high-voltage, cylindrical capacitorsto generate and deliver defibrillation shocks. For example, standard wetslug tantalum capacitors generally have a cylindrically shapedconductive casing serving as the terminal for the cathode and a tantalumanode connected to a terminal lead electrically insulated from thecasing. The opposite end of the casing is also typically provided withan insulator structure.

One such capacitor is shown and described in U.S. Pat. No. 5,369,547issued on Nov. 29, 1994 and entitled “Capacitor”. This patent disclosedan electrolytic capacitor that includes a metal container that functionsas a cathode. A porous coating, including an oxide of a metal selectedfrom the group consisting of ruthenium, iridium, nickel, rhodium,platinum, palladium, and osmium, is disposed proximate an inside surfaceof the container and is in electrical communication therewith. A centralanode selected from the group consisting of tantalum, aluminum, niobium,zirconium, and titanium is spaced from the porous coating, and anelectrolyte within the container contacts the porous coating and theanode.

U.S. Pat. No. 5,737,181 issued on Apr. 7, 1998 and entitled “Capacitor”describes a capacitor that includes a cathode material of the typedescribed in the above cited patent disposed on each of two opposedconducting plates. A metal anode (also of the type described in theabove cited patent) is disposed between the cathode material coating andthe conducting plates.

U.S. Pat. No. 5,982,609 issued Nov. 9, 1999 and entitled “Capacitor”describes a capacitor that includes a cathode having a porous coatingincluding an amorphous metal oxide of at least one metal selected fromthe group consisting of ruthenium, iridium, nickel, rhodium, rhenium,cobalt, tungsten, manganese, tantalum, molybdenum, lead, titanium,platinum, palladium, and osmium. An anode includes a metal selected fromthe group consisting of tantalum, aluminum, niobium, zirconium, andtitanium.

While the performance of these capacitors was acceptable fordefibrillator applications, efforts to optimize the mechanicalcharacteristics of the device have been limited by the constraintsimposed by the cylindrical design. In an effort to overcome this, flatelectrolytic capacitors were developed. U.S. Pat. No. 5,926,362 issuedon Jul. 20, 1999 and entitled “Hermetically Sealed Capacitor” describesa deep-drawn sealed capacitor having a generally flat, planar geometry.The capacitor includes at least one electrode provided by a metallicsubstrate in contact with a capacitive material. The coated substratemay be deposited on a casing side-wall or connected to a side-wall. Thecapacitor has a flat planar shape and utilizes a deep-drawn casingcomprised of spaced apart side-walls joined at their periphery by asurrounding intermediate wall. Cathode material is typically depositedon an interior side-wall of the conductive encasement which serves asone of the capacitor terminals; e.g. the cathode. The other capacitorterminal (the anode) is isolated from the encasement by aninsulator/feed-through structure comprised of, for example, aglass-to-metal seal. It is also known to deposit cathode material on aseparate substrate that is placed in electrical communication with thecase. In another embodiment, the cathode substrate is insulated from thecase using insulators and a separate cathode feed-through.

A valve metal anode made from metal powder is pressed and sintered toform a porous structure, and a wire (e.g. tantalum) is imbedded into theanode during pressing to provide a terminal for joining to thefeed-through. A separator (e.g. polyolefin, a fluoropolymer, a laminatedfilm, non-woven glass, glass fiber, porous ceramic, etc.) is providedbetween the anode and the cathode to prevent short circuits between theelectrodes. Separator sheets are sealed either to a polymer ring thatextends around the perimeter of the anode or to themselves.

A separate weld ring and polymer insulator may be utilized for thermalbeam protection as well as anode immobilization. Prior to encasementwelding, a separator encased anode is joined to the feed-through wireby, for example, laser welding. This joint is internal to the capacitor.The outer metal encasement structure is comprised essentially of twosymmetrical half shells that overlap and are welded at their perimeterseam to form a hermetic seal. After welding, the capacitor is filledwith electrolyte through a port in the encasement.

The above described techniques present concerns relating to both devicesize and manufacturing complexity. The use of overlapping half-shieldsresults in a doubling of the encasement thickness around the perimeterof the capacitor thus reducing the available interior space for thecapacitor's anode. This results in larger capacitors. Space for theanode material is further reduced by the presence of the weld ring andspace insulator. In addition, manufacturing processes become morecomplex and therefore more costly, especially in the case of adeep-drawn encasement.

A further disadvantage of the known design involves the complexity ofthe anode terminal-to-feed-through terminal weld joint. As wasdescribed, a tantalum anode lead is imbedded into the anode and isjoined via laser welding to a terminal lead of the feed-through. This istypically accomplished by forming a “J” or “U” shape with one or more ofthe leads, pressing the terminal end of these leads together, and laserwelding the interface. In order to accomplish this, one must eitherperform this step prior to welding the feed-through ferrule into theencasement or sufficient space must be provided in the capacitor anodestructure to facilitate clamping and welding while the anode is in thecase. This results in additional manufacturing complexity while thelatter negatively impacts device size.

As stated previously, a separator material is provided on the anode andmay be sealed to itself to form an envelope. The anode is typically onthe order of 0.1 inch thick. As a result, the sealing operation iscomplex, and significant separator material typically overhangs theanode. This overhang must be accommodated in the design and typicallyeither reduces the size of the anode or increases the size of thecapacitor. Furthermore, due to the proximity of thermally sensitiveseparator material to the encasement, the separator is in direct contactwith the cathode/encasement structure. Weld parameters must therefore becarefully selected to prevent thermal damage of the separator material.When cathode material is deposited on a separate substrate, as describedabove, substrate thickness further reduces the space available for anodematerial or increases the size of the capacitor.

Thus, while the development of flat electrolytic capacitorssignificantly reduces size and thickness, defibrillation capacitors arestill the largest components in current ICDs making further downsizing aprimary objective.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a capacitorstructure, comprising a shallow drawn encasement having first and secondmajor sides and a peripheral wall coupled to first and second majorsides. First and second anodes are positioned within encasementproximate interior surfaces of the first and second major sidesrespectively. A cathode is positioned within encasement intermediate thefirst and second anodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 is a cross-sectional view of an electrolytic capacitor inaccordance with the teachings of the prior art;

FIGS. 2, 3, and 4 are front, side, and top cross-sectional views of aflat electrolytic capacitor in accordance with the teachings of theprior art;

FIGS. 5, 6, and 7 are front cross-sectional, side cross-sectional, andscaled cross-sectional views of a novel electrolytic capacitor;

FIG. 8 is a cross-sectional view of a capacitor/anode encasementstructure in accordance with the teachings of the prior art;

FIG. 9 is a cross-sectional view of a novel capacitor/anode encasementassembly;

FIG. 10 is a cross-sectional view of an alternative capacitor/anodeencasement assembly;

FIG. 11 is a cross-sectional view of a yet another embodiment of thepresent invention utilizing a central cathode sandwiched between firstand second anodes;

FIG. 12 illustrates the embodiment shown in FIG. 11 configured in acase-negative configuration; and

FIG. 13 illustrates the embodiment shown in FIG. 11 configured in a caseneutral configuration.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the invention is merely exemplaryin nature and is not intended to limit the scope, applicability, orconfiguration of the invention in any way. Rather, the followingdescription provides a convenient illustration for implementingexemplary embodiments of the invention. Various changes to the describedembodiments may be made in the function and arrangement of the elementsdescribed herein without departing from the scope of the invention.

FIG. 1 is a cross-sectional view of an electrolytic capacitor inaccordance with the teaching of the prior art. It comprises acylindrical metal container 20 made of, for example tantalum. Typically,container 20 comprises the cathode of the electrolytic capacitor andincludes a lead 22 that is welded to the container. An end seal of cap24 includes a second lead 26 that is electrically insulated from theremainder of cap 24 by means of a feed-through assembly 28. Cap 24 isbonded to container 20 by, for example, welding. Feed-through 28 of lead26 may include a glass-to-metal seal through which lead 26 passes. Ananode 30 (e.g., porous sintered tantalum) is electrically connected tolead 26 and is disposed within container 20. Direct contact betweencontainer 20 and anode 30 is prevented by means of electricallyinsulating spacers 32 and 34 within container 20 that receive oppositeends of anode 30. A porous coating 36 is formed directly on the innersurface of container 20. Porous coating 36 may include an oxide ofruthenium, iridium, nickel, rhodium, platinum, palladium, or osmium. Asstated previously, anode 30 may be made of a sintered porous tantalum.However, anode 30 may be aluminum, niobium, zirconium, or titanium.Finally, an electrolyte 38 is disposed between and in contact with bothanode 30 and cathode coating 36 thus providing a current path betweenanode 30 and coating 36. As stated previously, while capacitors such asthe one shown in FIG. 1 were generally acceptable for defibrillatorapplications, optimization of the device is limited by the constraintsimposed by the cylindrical design.

FIGS. 2, 3, and 4 are front, side, and top cross-sectional viewsrespectively of a flat electrolytic capacitor, also in accordance withthe teachings of the prior art, designed to overcome some of thedisadvantages associated with the electrolytic capacitor shown in FIG.1. The capacitor of FIGS. 2, 3, and 4 comprises an anode 40 and acathode 44 housed inside a hermetically sealed casing 46. The capacitorelectrodes are activated and operatively associated with each other bymeans of an electrolyte contained inside casing 46. Casing 46 includes adeep drawn can 48 having a generally rectangular shape and comprised ofspaced apart side-walls 50 and 52 extending to and meeting with opposedend walls 54 and 56 extending from a bottom wall 58. A lid 60 is securedto side-walls 50 and 52 and to end walls 54 and 56 by a weld 62 tocomplete an enclosed casing 46. Casing 46 is made of a conductive metaland serves as one terminal or contact for making electrical connectionsbetween the capacitor and its load.

The other electrical terminal or contact is provided by a conductor orlead 64 extending from within the capacitor through casing 46 and, inparticular, through lid 60. Lead 64 is insulated electrically from lid60 by an insulator and seal structure 66. An electrolyte fill opening 68is provided to permit the introduction of an electrolyte into thecapacitor, after which opening 68 is closed. Cathode electrode 44 isspaced from the anode electrode 40 and comprises an electrode activematerial 70 provided on a conductive substrate. Conductive substrate 70may be selected from the group consisting of tantalum, nickel,molybdenum, niobium, cobalt, stainless steel, tungsten, platinum,palladium, gold, silver, cooper, chromium, vanadium, aluminum,zirconium, hafnium, zinc, iron, and mixtures and alloys thereof. Anode40 may be selected from the group consisting of tantalum, aluminum,titanium, niobium, zirconium, hafnium, tungsten, molybdenum, vanadium,silicon, germanium, and mixtures thereof. A separator structure includesspaced apart sheets 72 and 74 of insulative material (e.g. a microporouspolyolefinic film). Sheets 72 and 74 are connected to a polymeric ring76 and are disposed intermediate anode 40 and coated side-walls 50 and52 which serve as a cathode electrode.

As already mentioned, the above described capacitors present certainconcerns with respect to device size and manufacturing complexity. Incontrast, FIGS. 5, 6, and 7 are front cross-sectional, sidecross-sectional, and scaled cross-sectional views of an electrolyticcapacitor suitable for use in an implantable medical device. As can beseen, one or more layers of an insulative polymer separator material 142(e.g. micro-porous PTFE or polypropylene) are heat sealed around a thin,D-shaped anode 140 (e.g. tantalum) having an anode lead wire 144 (e.g.tantalum) embedded therein. Capacitor grade tantalum powder such as the“NH” family of powders may be employed for this purpose. These tantalumpowders have a charge per gram rating of between approximately 17,000 to23,000 microfarad-volts/gram and have been found to be well suited forimplantable cardiac device capacitor applications. Tantalum powders ofthis type are commercially available from HC Starck, Inc. located inNewton, Mass.

Before pressing, the tantalum powder is typically, but not necessarily,mixed with approximately 0 to 5 percent of a binder such as ammoniumcarbonate. This and other binders are used to facilitate metal particleadhesion and die lubrication during anode pressing. The powder andbinder mixture are dispended into a die cavity and are pressed to adensity of approximately 4 grams per cubic centimeter to approximately 8grams per cubic centimeter. After pressing, it is sometimes beneficialto modify anode porosity to improve conductivity within the internalportions of the anode. Porosity modification has been shown tosignificantly reduce resistance. Macroscopic channels are incorporatedinto the body of the anodes to accomplish this. Binder is then removedfrom the anodes either by washing in warm deionized water or by heatingat a temperature sufficient to decompose the binder. Complete binderremoval is desirable since residuals may result in high leakage current.Washed anodes are then vacuum sintered at between approximately 1,350degrees centigrade and approximately 1,600 degrees centigrade topermanently bond the metal anode particles.

An oxide is formed on the surface of the sintered anode by immersing theanode in an electrolyte and applying a current. The electrolyte includesconstituents such as water and phosphoric acid and perhaps other organicsolvents. The application of current drives the formation of an oxidefilm that is proportional in thickness to the targeted forming voltage.A pulsed formation process may be used wherein current is cyclicallyapplied and removed to allow diffusion of heated electrolyte from theinternal pores of the anode plugs. Intermediate washing and annealingsteps may be performed to facilitate the formation of a stable, defectfree, oxide.

Layers of cathode material 146 are deposited on the inside walls of athin, shallow drawn, D-shaped casing 148 (e.g. titanium) having firstand second major sides and a peripheral wall, each of which have aninterior surface. The capacitive materials may be selected from thosedescribed above or selected from the group including graphitic or glassycarbon on titanium carbide, carbon and silver vanadium oxide on titaniumcarbide, carbon and crystalline manganese dioxide on titanium carbide,platinum on titanium, ruthenium on titanium, barium titanate ontitanium, carbon and crystalline ruthenium oxide on titanium carbide,carbon and crystalline iridium oxide on titanium carbide, silvervanadium oxide on titanium and the like.

Anode 140 and cathode material 146 are insulated from each other bymeans of a micro-porous polymer separator material such as a PTFEseparator of the type produced by W. L. Gore, Inc. located in Elkton,Md. or polypropylene of the type produced by Celgard, Inc. located inCharlotte, N.C. Separators 146 prevent physical contact and shorting andalso provide for ionionic conduction. The material may be loosely placedbetween the electrodes or can be sealed around the anode and/or cathode.Common sealing methods include heat sealing, ultra sonic bonding,pressure bonding, etc.

The electrodes are housed in a shallow drawn, typically D-shaped case(e.g. titanium) that may have a material thickness of approximately0.005 to 0.016 inches thick. A feed-through 150 is comprised of aferrule 154 (e.g. titanium), a terminal lead wire 152 (e.g. tantalum),and an insulator 156 (e.g. a polycrystalline ceramic polymer,non-conducting oxides, conventional glass, etc.) is bonded to ferrule154 and lead wire 152. Sealed anode 140 is inserted into a cathodecoated case and spacer ring is inserted around the periphery of theanode to secure the position of the anode within the case. A J-shapedfeed-though lead wire 152 is electrically coupled to anode lead wire 144as, for example, by resistance or laser welding. In accordance with anaspect of the present invention, lead wire 152 may be joined to anodelead wire 144 without the necessity for a J-shaped bend as will be fullydescribed hereinbelow.

After assembly and welding, an electrolyte is introduced into the casingthrough a fill-port 160. The electrolyte is a conductive liquid having ahigh breakdown voltage that is typically comprised of water, organicsolvents, and weak acids or of water, organic solvents and sulfuricacid. Filling is accomplished by placing the capacitor in a vacuumchamber such that fill-port 160 extends into a reservoir of electrolyte.When the chamber is evacuated, pressure is reduced inside the capacitor.When the vacuum is released, pressure inside the capacitorre-equilibrates, and electrolyte is drawn through fill-port 160 into thecapacitor.

Filled capacitors are aged to form an oxide on the anode leads and otherareas of the anode. Aging, as with formation, is accomplished byapplying a current to the capacitor. This current drives the formationof an oxide film that is proportional in thickness to the targeted agingvoltage. Capacitors are typically aged approximately at or above theirworking voltage, and are held at this voltage until leakage currentreaches a stable, low value. Upon completion of aging, capacitors arere-filled to replenish lost electrolyte, and the fill-port 160 is sealedas, for example, by laser welding a closing button or cap over theencasement opening.

As stated previously, the outer metal encasement structure of a knownplanar capacitor generally comprises two symmetrical half shells thatoverlap and are then welded along their perimeter seam to form ahermetic seal. Such a device is shown in FIG. 8. That is, the encasementcomprises a case 164 and an overlapping cover 166. A separator sealedanode 168 is placed within case 164, and a polymer spacer ring 170 ispositioned around the periphery of anode assembly 168. Likewise, a metalweld ring 172 is positioned around the periphery of spacer ring 170proximate the overlapping portion 174 of case 164 and cover 166. Theoverlapping portions of case 164 and cover 166 are then welded along theperimeter seam to form a hermetic seal.

This technique presents certain concerns relating to both device sizeand manufacturing complexity. The use of overlapping half-shieldsresults in a doubling of the encasement thickness around the perimeterof the capacitor thus reducing the available interior space for theanode. Thus, for a given size anode, the resulting capacitor is larger.Furthermore, space for anode material is reduced due to the presence ofweld ring 172 and insulative polymer spacer ring 170. This device ismore complex to manufacture and therefore more costly.

FIG. 9 is a cross-sectional view illustrating one of the novel aspectsof the present invention. In this embodiment, the encasement iscomprised of a shallow drawn case 176 and a cover or lid 178. Thisshallow drawn encasement design uses a top down welding approach.Material thickness is not doubled in the area of the weld seam as wasthe situation in connection with the device shown in FIG. 8 thusresulting in additional space for anode material.

Cover 178 is sized to fit into the open side of shallow drawn metal case176. This results in a gap (e.g. from 0 to approximately 0.002 inches)in the encasement between case 176 and cover 178 that could lead to thepenetration of the weld laser beam thus potentially damaging thecapacitor's internal components. To prevent this, a metalized polymericweld ring is placed or positioned around the periphery of anode 168.Weld ring 180 is somewhat thicker than the case to cover gap 182 tomaximize protection. Metalized weld ring 180 may comprise a polymerspacer 186 having a metalized surface 184 as shown. Metalized weld ring180 provides for both laser beam shielding and anode immobilization. Themetalized polymer spacer 180 need only be thick enough to provide abarrier to penetration of the laser beam and is sacrificial in nature.This non-active component substantially reduces damage to the activestructures on the capacitor.

Metalized polymer spacer 180 is placed around the perimeter of anode 168during assembly and may be produced my means of injection molding,thermal forming, tube extrusion, die cutting of extruded or cast films,etc. Spacer 180 may be provided through the use of a pre-metalizedpolymer film. Alternatively, the metal may be deposited during aseparate process after insulator production. Suitable metallizationmaterials include aluminum, titanium, etc. and mixtures and alloys.

FIG. 10 is a cross-sectional view illustrating an alternative to theembodiment shown in FIG. 9. Again, the encasement comprises a case 176and a cover or lid 178 resulting in gap 182. The anode assembly 168 ispositioned within the encasement as was the situation in FIG. 9. Toprotect the capacitor's internal components from damage due to the weldlaser beam, a metalized tape 184 is positioned around the perimeter ofanode 168.

The embodiments shown in FIGS. 9 and 10 not only have space savingaspects in the encasement design, but the components are simple andinexpensive to produce. The top down assembly facilitates fabricationand welding processes. The thinness of the weld ring/spacer 180 ormetalized tape 184 reduces the need for additional space around theperimeter of the capacitor thus improving energy density. The designlends itself to mass production methods and reduces costs, componentcount, and manufacturing complexity.

FIG. 11 illustrates an embodiment of the present invention utilizingfirst and second anodes and a central cathode. Like reference numeralsdenote like elements. As stated previously, prior art designs utilize aseparator material on the anode that is sealed to itself to form anenvelope. The sealing operation is complex, and a significant amount ofseparator material typically overhangs the anode. The overhang must beaccommodated within the capacitor's encasement and therefore reduces thesize of the anode. Therefore, for an equal size anode, the overallcapacitor size is increased. The thermally sensitive separator materialmay be in direct contact with the cathode/encasement structure, andtherefore, weld parameters must be carefully selected to prevent thermaldamage to the separator material. If cathode, material is deposited on aseparate substrate, the substrate thickness further reduces the spaceavailable for anode material thus potentially increasing the size of thecapacitor.

Referring to FIG. 11, a central cathode substrate 202 is positionedbetween first and second anodes 204 and 206 respectively. In order tooptimize the energy density of the electrolytic capacitor, the cathodecapacitance must be several orders of magnitude higher than that ofanodes 204 and 206. In the past, this was accomplished by incorporatingthin, etched aluminum foils between many anode layers, thus providing alarge planar surface area and high capacitance. However, in order topromote downsizing as described above, the present invention employsmaterials of a high specific capacitance rather than large planar area.The capacitive materials may be selected from those described above. Asealing separator 208 is formed around cathode substrate 202 to form anenvelope; however, in this case, the sealing envelope is significantlythinner than is the case when utilizing a central anode. Sealingseparator 208 may comprise one or more of the materials described above.Common sealing methods include heat sealing, ultrasonic bonding,pressure bonding, etc. Since cathode substrate 202 can be coated on bothsides with cathode material, the use of two cathode substrates generallynecessary in capacitors employing a single central anode is avoided.Finally, first and second insulative layers (e.g. a polymer) 210 and 212respectfully insulate anodes 204 and 206 respectively from the sidewallsof encasement 148.

FIG. 12 illustrates the multi-anode electrode stack shown in FIG. 11positioned within an encasement comprised of the shallow drawn case 176and cover or lid 178 as was shown in connection with FIG. 9 and FIG. 10.Again, like reference numerals denote like elements. As was describedearlier, it is not uncommon for the encasement of the capacitor itselfto serve as the cathode electrode. This is accomplished in theembodiment shown in FIG. 12 by connecting cathode substrate 202 to theencasement as is shown at 214. Alternatively, the encasement may be madeelectrically neutral by not coupling cathode substrate 202 to theencasement. Cathode substrate 202 may simply be sealed within separators208 as is shown at 216 in FIG. 13. In this situation, however, it isnecessary not only to provide access to an anode electrode at theexterior of encasement 148, but provisions must also be made to access acathode electrode from the exterior of the capacitor.

While the multi-anode electrode stack has been shown and described asincluding first and second anodes and an intermediate cathode, it shouldbe clear that a plurality of cathodes may be utilized each onepositioned between adjacent anodes.

Thus, there has been provided a dual-anode electrolytic capacitor thatis easy to manufacture and smaller for a given capacitance. Theinventive capacitor is therefore suitable for use in implantable medicaldevices such as defibrillators, even as such devices become smaller andsmaller.

What is claimed is:
 1. A capacitor structure comprising: a shallow drawnencasement having first and second major sides and a peripheral wallcoupled to said first and second major sides; first and second anodespositioned within said encasement proximate interior surfaces of saidfirst and second major sides respectively; a cathode positioned withinsaid encasement intermediate said first and second anodes, said cathodeelectrically coupled to said encasement; and a first separator forinsulating said cathode from said first and second anodes.
 2. Acapacitor structure according to claim 1 further comprising a secondseparator for insulating said fist and second anodes from saidencasement.
 3. A capacitor structure according to claim 2 wherein saidcathode comprises a substrate having cathode material deposited thereon.4. A capacitor structure according to claim 3 wherein said cathodematerial comprises carbon and said substrate is formed from titaniumcarbide.
 5. A capacitor structure according to claim 3 wherein saidcathode material comprises carbon and silver vanadium oxide and saidsubstrate is formed from titanium carbide.
 6. A capacitor structureaccording to claim 3 wherein said cathode material comprises carbon andcrystalline manganese dioxide and said substrate is formed from titaniumcarbide.
 7. A capacitor structure according to claim 3 wherein saidcathode material comprises platinum and said substrate is formed fromtitanium.
 8. A capacitor structure according to claim 3 wherein saidcathode material comprises ruthenium and said substrate material isformed from titanium.
 9. A capacitor structure according to claim 3wherein said cathode material comprises silver vanadium oxide and saidsubstrate is formed from titanium.
 10. A capacitor structure accordingto claim 3 wherein said cathode material comprises barium titanate andsaid substrate is formed from titanium.
 11. A capacitor structureaccording to claim 3 wherein said cathode material comprises carbon andcrystalline ruthenium oxide and said substrate is formed from titaniumcarbide.
 12. A capacitor structure according to claim 3 wherein saidcathode material comprises carbon and crystalline iridium oxide and saidsubstrate is formed from titanium carbide.
 13. A capacitor structureaccording to claim 3 wherein said cathode material is deposited on firstand second opposite sides of said substrate.
 14. A capacitor structureaccording to claim 3 further comprising an insulative feed-through insaid encasement through which electrical coupling may be made to saidfirst and second anodes.
 15. A capacitor structure according to claim 14wherein said feed-through is made of a polymeric material.
 16. Acapacitor structure according to claim 15 wherein said feed-throughforms a hermetic seal with said encasement.
 17. A capacitor structureaccording to claim 3 wherein said encasement comprises: a shallow drawncase comprising: said first major side and said peripheral wall; and alid including said second major side and sealingly coupled to said casealong adjacent edges of said lid and said wall.
 18. A capacitorstructure according to claim 3 further comprising a protective layer onat least one of said first and second anodes adjacent said peripheralwall to protect said at least one of said first and second anodes whensaid lid is sealingly coupled to said case.
 19. A capacitor structureaccording to claim 18 wherein said protective layer comprises ametalized ring.
 20. A capacitor structure according to claim 19 whereinsaid metalized ring comprises a polymer spacer having a metalizedsurface.
 21. A capacitor structure according to claim 18 wherein saidprotective layer comprises a metalized tape.
 22. A capacitor for use inan implantable medical device, said capacitor comprising: a shallowdrawn encasement having first and second major sides and a peripheralwall coupled to said first and second major sides; first and secondanodes positioned within said encasement proximate interior surfaces ofsaid first and second major sides respectively; a cathode positionedwithin said encasement intermediate said first and second anodes; anelectrolyte within said encasement and in contact with said cathode andsaid first and second anodes; a first separator for insulating saidcathode from said first and second anodes; a second separator forinsulating said first and second anodes from said encasement; and aninsulative feed-through in said encasement through which electricalcoupling may be made to said first and second anodes.
 23. A capacitorstructure according to claim 22 wherein said cathodes is electricallycoupled to said encasement.
 24. A capacitor structure according to claim23 wherein said cathode comprises a substrate having cathode materialdeposited thereon.
 25. A capacitor structure according to claim 24wherein said cathode material is deposited on first and second oppositesides of said substrate.
 26. A capacitor structure according to claim 22wherein said feed-through is made of a polymeric material.
 27. Acapacitor structure according to claim 26 wherein said feed-throughforms a hermetic seal with said encasement.
 28. A capacitor structureaccording to claim 22 wherein said encasement comprises: a shallow drawncase comprising: said first major side and said peripheral wall; and alid including a second major side and sealingly coupled to said casealong adjacent edges of said lid and said wall.
 29. A capacitorstructure according to claim 28 further comprising a protective layer onat least one of said first and second anodes adjacent said peripheralwall to protect said at least one of said first and second anodes whensaid lid is sealingly coupled to said case.